The Genus Conradina (Lamiaceae): a Review
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plants Review The Genus Conradina (Lamiaceae): A Review Noura S. Dosoky 1 and William N. Setzer 1,2,* 1 Aromatic Plant Research Center, 615 St. George Square Court, Suite 300, Winston-Salem, NC 27103, USA; [email protected] 2 Department of Chemistry, University of Alabama in Huntsville, Huntsville, AL 35899, USA * Correspondence: [email protected]; Tel.: +1-256-824-6519 Received: 24 February 2018; Accepted: 10 March 2018; Published: 11 March 2018 Abstract: Conradina (Lamiaceae) is a small genus of native United States (US) species limited to Florida, Alabama, Mississippi, Tennessee and Kentucky. Three species of Conradina are federally listed as endangered and one is threatened while two are candidates for listing as endangered. The purpose of the present review is to highlight the recent advances in current knowledge on Conradina species and to compile reports of chemical constituents that characterize and differentiate between Conradina species. Keywords: Conradina; essential oil; ursolic acid; cytotoxicity; antimicrobial; antileishmanial; phylogenetic analysis 1. Introduction Conradina A. Gray (Lamiaceae) is a small genus of morphologically distinctive, narrow-leaved, minty-aromatic shrubs endemic to the southeastern United States of America (USA) [1]. It consists of six to nine US native species. According to the Plant List database [2] and Integrated Taxonomic Information Species (ITIS), the acceptable number of species for the genus is only six (Conradina canescens A. Gray, C. cygniflora C.E. Edwards, Judd, Ionta & Herring, C. etonia Kral & McCartney, C. glabra Shinners, C. grandiflora Small and C. verticillata Jennison) while C. brevifolia Shinners, C. montana Small and C. puberula Small are considered synonyms of other species. The Missouri Botanical Garden, however, lists nine distinct species [3]. Conradina species are characterized by very dense hairs on their lower leaf surfaces and by a sharply bent corolla tube in the flowers [1,4]. Asa Gray established the genus Conradina in 1870, named for the American botanist Solomon White Conrad [5]. Conradina species grow well in xeric habitats with well-drained sandy soils. It is thought that Conradina may be a pioneer species in disturbed areas since it has the ability to colonize xeric disturbed habitats [1,5]. Each species of Conradina occupies a separate geographical region [1,6]. Five of the species are endemic to Florida, one is native to west Florida, south Alabama, and south Mississippi, and one is endemic to north-central Tennessee and Kentucky (Figure1). Due to habitat destruction from residential, commercial, and agricultural land conversions and their very restricted distribution, three of these species are on the United States Fish and Wildlife Service (USFWS) federal list as endangered (Conradina brevifolia, C. glabra, and C. etonia)[5], one as threatened (C. verticillata)[6] and two species are considered candidates for listing as endangered (C. grandiflora and C. cygniflora). The aim of the present review is to summarize the literature in order to document secondary metabolites that characterize and differentiate between Conradina species. We shall also assess the reported biological activities of Conradina species, with particular focus on their phylogenetic affinities and anti-microbial, anti-leishmanial and cytotoxic properties. Plants 2018, 7, 19; doi:10.3390/plants7010019 www.mdpi.com/journal/plants Plants 2018, 7, 19 2 of 10 Plants 2018, 7, 19 2 of 10 FigureFigure 1. 1.Locations Locations of of known known populations populations of ofConradina Conradinaspecies. species. 2.2. Description Description ConradinaConradinarepresents represents a a group group of of evergreen, evergreen, compact, compact, perennial perennial shrubs shrubs with with virgate virgate branches. branches. LeavesLeaves are are aromatic aromatic and and needle-likeneedle-like withwith narrow,narrow, entire, revolute leaf-blades. Flowers Flowers are are solitary solitary or orin in a agroup group of of few few in inaxillary axillary cymes. cymes. The The calyx calyx is two-lipped; is two-lipped; the thelower lower lip has lip hastwo twolong, long, narrow narrow lobes lobeswhile while the upper the upper lip has lip hasthree three short short broad broad lobes. lobes. Corolla Corolla is white is white to purple to purple in color, in color, two-lipped; two-lipped; the thelower lower lip lip has has three three lobes lobes and and usually usually dotted dotted whil whilee the the upper upper lip lip is iserect erect and and slightly slightly concave. concave. ConradinaConradina canescens canescensA. A. Gray Gray (false (false rosemary) rosemary) is is the the only only species species of of this this genus genus that that is is relatively relatively commoncommon in in its its range range and and the the most most morphologically morphologically variable variable (Table (Table1) 1). It. It is is native native to to a a small small area area of of westwest Florida Florida and and south south Alabama Alabama and and southern southern parts parts of of Mississippi Mississippi [ 7[7].]. It It occurs occurs on on sunny, sunny, dry dry sand sand soilssoils on on coastal coastal dunes, dunes, inin sandsand scrubsscrubs and in dry longleaf longleaf pineland pineland ecosystems. ecosystems. It Itshows shows tolerance tolerance for forthe the heat heat and and humidity humidity of of the the Southeast Southeast and and is consideredconsidered aa drought-tolerantdrought-tolerant landscapelandscape plant plant that that growsgrows best best in in lean, lean, sandy sandy soils soils [8]. [8].C. canescensC. canescensis one is one of the of indicatorthe indicator species species for wooded for wooded dunes dunes [9] and [9] isand an excellentis an excellent candidate candidate for restoration for restoration of coastal of areas.coastal It areas. can be It used can be for used beach for projects beach thatprojects require that plantingrequire onplanting the back on sidethe back of primary side of dunes,primary or dunes, any side or ofany secondary side of secondary dunes. It hasdunes. also It been has also used been in gardensused in asgardens a groundcover as a groundcover as the branches as the branches can reach can up reach to 1 m up in to spread. 1 m in Falsespread. rosemary False rosemary was easily was propagatedeasily propagated in the University in the University of Florida of InstituteFlorida Institute of Food of and Food Agricultural and Agricultural Sciences Sciences Extension Extension using softwoodusing softwood stem cuttings stem cuttings from terminal from terminal shoots taken shoots during taken theduring growing the growing season. season. Morphologically,Morphologically,C. C. brevifolia brevifoliaShinners Shinners (short-leaved (short-leaved rosemary) rosemary) is is very very similar similar to toC. C. canescens canescens, , differingdiffering by by its its shorter shorter leaves leaves and and greater greater number number of of flowers flowers per per axil, axil, and and it it is is also also similar similar to to the the endangeredendangeredC. C. glabra glabra[ 1[1,5].,5]. C.C. brevifoliabrevifolia waswas describeddescribed asas aa newnew speciesspecies byby Shinners Shinners [ 4[4].]. Many Many taxonomictaxonomic reviews reviews of ofConradina Conradinahave have upheld upheldC. C. brevifolia brevifoliaas as a a distinct distinct species species yet yet it it is is taxonomically taxonomically questionablequestionable[1 ,[1,6,10,11].6,10,11]. Some Some taxonomists taxonomists are stillare uncertainstill uncertain that C. that brevifolia C. brevifoliais a true is different a true different species andspecies therefore and therefore they treat they it as treat a synonym it as a synonym to C. canescens. to C. canescens. C. brevifolia C. brevifoliahas a very has restricted a very restricted range in range the middlein the ofmiddle the Lake of the Wales Lake Ridge Wales in Central Ridge Floridain Central [12 –Florida14] and [12–14] has been and listed has as been a federally listed as endangered a federally speciesendangered in 1993 species [5]. Habitat in 1993 destruction [5]. Habitat for destruction agricultural for and agricultural residential and purposes residential is the mainpurposes threat is tothe thismain species. threat to this species. C.C. etonia etoniaKral Kral & & McCartney McCartney (Etonia (Etonia rosemary) rosemary) was was discovered discovered in in the the Etonia Etonia Scrub Scrub in in Putnam Putnam County,County, Florida Florida in in September September 1990 1990 and and describeddescribed asas aa newnew speciesspecies in 1991 [6]. [6]. C.C. etonia etonia isis similar similar to toC.C. grandiflora grandiflora inin general general appearance appearance and and the the flowers flowers are are large large and and quite quite similar similar but but the the leaves leaves of of C. C.etonia etonia areare broader broader than than C.C. grandiflora grandiflora and have clearly visible laterallateral veinsveins onon thethe lowerlower surface surface [ 1[1,15].,15]. C. etonia is found in very limited areas of deep white sand scrub dominated by sand pines (Pinus clausa) and scrubby oaks (Quercus spp.) on dry soils. Its entire known range is within a subdivision Plants 2018, 7, 19 3 of 10 C. etonia is found in very limited areas of deep white sand scrub dominated by sand pines (Pinus clausa) and scrubby oaks (Quercus spp.) on dry soils. Its entire known range is within a subdivision of Putnam County containing streets and a few residences, which make it